gr8fulpete,
no, I use line in (analog) on the D50. If you want to connect both devices digitally, you need a converter that does two things:
1) convert the electrical AES-out of the MixPre D to optical (D50): easy
2) convert AES digital signal to SPDIF: not so easy, since some important bits have a different meaning (especially the copy protect bit!) and the D50 probably rejects the AES signal.
Hope its clear now. BTW setting levels as described by me is unnecessary for a digital connection!
Greetings,
Rainer